Longitudinal study assessing the return of chloroquine susceptibility of Plasmodium falciparum in isolates from travellers returning from West and Central Africa, 2000-2011

Abstract

Background: Chloroquine (CQ) was the main malaria therapy worldwide from the 1940s until the 1990s. Following the emergence of CQ-resistant Plasmodium falciparum, most African countries discontinued the use of CQ, and now promote artemisinin-based combination therapy as the first-line treatment. This change was generally initiated during the last decade in West and Central Africa. The aim of this study is to describe the changes in CQ susceptibility in this African region, using travellers returning from this region as a sentinel system.

Methods: The study was conducted by the Malaria National Reference Centre, France. The database collated the pfcrtK76T molecular marker for CQ susceptibility and the in vitro response to CQ of parasites from travellers' isolates returning from Senegal, Mali, Ivory Coast or Cameroon. As a proxy of drug pressure, data regarding CQ intake in febrile children were collated for the study period. Logistic regression models were used to detect trends in the proportions of CQ resistant isolates.

Results: A total of 2874 parasite isolates were genotyped between 2000-2011. The prevalence of the pfcrt76T mutant genotype significantly decreased for Senegal (from 78% to 47%), Ivory Coast (from 63% to 37%), Cameroon (from 90% to 59%) and remained stable for Mali. The geometric mean of the 50% inhibitory concentration (IC50) of CQ in vitro susceptibility and the proportion of resistant isolates (defining resistance as an IC50 value > 100 nM) significantly decreased for Senegal (from 86 nM (59%) to 39 nM (25%)), Mali (from 84 nM (50%) to 51 nM (31%)), Ivory Coast (from 75 nM (59%) to 29 nM (16%)) and Cameroon (from 181 nM (75%) to 51 nM (37%)). Both analyses (molecular and in vitro susceptibility) were performed for the 2004-2011 period, after the four countries had officially discontinued CQ and showed an accelerated decline of the resistant isolates for the four countries. Meanwhile, CQ use among children significantly deceased in this region (fixed effects slope = -0.3, p < 10-3).

Conclusions: An increase in CQ susceptibility following official withdrawal of the drug was observed in travellers returning from West and Central African countries. The same trends were observed for molecular and in vitro analysis between 2004-2011 and they correlated to the decrease of the drug pressure.

Figure 1

Imported malaria infection from West and Central Africa reported in the French Malaria Surveillance system. Number of Plasmodium falciparum infections diagnosed in travellers returning to France from Senegal, Mali, Ivory Coast and Cameroon notified to the National Reference Centre for Malaria (CNRpalu), Paris, France, from 2000 to 2011.

Figure 2

Evolution of the prevalence of pfcrt76T isolates after the CQ ban in different African regions. Observed and fitted (by logistic regression) prevalence of pfcrt76 mutant isolates and 95% Confidence Interval, from travellers returning to France from A) Senegal, B) Mali C) Ivory Coast, and D) Cameroon, from 2004 to 2011, after that most African countries officially banned the use of CQ. The slopes and their standard error are displayed for each country. Each spot represents the number of isolates per year for travellers’ data and per study for field studies. The size of the spot is proportional to the number of isolates. The p-value indicates whether the slope of the predicted line is significantly different from zero (data from CNRpalu, France). These data are compared with two field studies E) in Malawi and F) Kenya after the CQ ban (1993 for Malawi and 1999 for Kenya) [14,16].

Figure 3

Evolution of in vitro anti-malarial drug response in imported malaria. A generalized linear model is fitted to the in vitro data A: chloroquine response (IC₅₀), B: desethylamodiaquine response, C: mefloquine response, D: lumefantrine response, for clinical isolates collected from travellers returning to France from Senegal, Mali, Ivory Coast, and Cameroon, from 2004 to 2011. Slopes, standard errors and the p-value indicating whether the slope of the predicted line is significantly different from zero are displayed (data from CNRpalu, France). Each spot represents the geometric mean IC₅₀ per year and the size of the spot is proportional to the number of isolates.

Figure 4

Evolution of the prevalence of pfcrt76 mutant isolates regarding the change in drug use, 2000–2011. The Y-axis represents the observed (red crosses) and fitted (by logistic regression, red line) prevalence of pfcrt76 mutant isolates from travellers returning to France from Senegal, Mali, Ivory Coast and Cameroon, from 2000 to 2011 (data from CNRpalu, France). The Z-axis represents observed (blue upward triangle) and fitted (by logistic regression using linear mixed model, blue line) prevalence of CQ use among fever in children under five years-old with fever in Senegal, Mali, Ivory Coast and Cameroon, from 2000 to 2011 (data from Demographic Health Survey and Multiple Indicator Cluster Survey).